1. Technical Field
This disclosure relates to semiconductor devices and more particularly, to a method and apparatus for preventing formation of black silicon on wafers.
2. Description of the Related Art
Etching processes remove material from a substrate by, for example chemically reacting a portion of a surface to be removed. During etching, however, the material being etched frequently is redeposited which is generally undesirable. In the semiconductor industry, etching is used extensively in processing integrated circuit chips. Silicon wafers are used in the fabrication process of integrated circuit chips as a substrate on which semiconductor devices are formed. In integrated circuits that include memory cells, capacitors such as deep trench capacitors require etching the deep trenches into the silicon substrate. This etching typically promotes redeposition of the silicon material in other areas of the wafer. These other areas include a back surface and edges of the silicon wafer.
Black silicon is a term used to describe silicon deposits formed by etching silicon in semiconductor chips. Black silicon typically takes the form of small spikes which are usually between about 4 to 6 microns in length. These spikes often form on the exposed areas of the silicon substrate and in particular form along the outer edges of the wafer. The spikes can break away from the wafer and interfere with the formation of devices on the wafer during processing. The presence of the spikes effects chip yield.
As mentioned above, the spikes are often formed on the edges and back surface of the wafer. Conventional techniques have attempted to remove the spikes prior to additional processing by rinsing the back surface of the wafer or by performing an edge bead removal. The rinsing technique uses a fluid to rinse away the spikes formed on the wafer edges and/or the back surface. While the edge bead removal uses a mechanical process such as polishing to remove these spikes. Both techniques, however, do not insure that spikes are not present in critical areas of the chip during processing.
Therefore, a need exists for preventing the formation of black silicon during fabrication of semiconductor chips. A further need exists for increasing chip yield by the elimination of black silicon deposition.